Chain saw guide bar equipped with chain tensioner

Abstract

A chain saw guide bar has self-contained mechanism to force movement of the guide bar away from a drive sprocket to tension the saw chain. The mechanism includes a bearing surface that engages a mounting stud on the chain saw housing and a rotatable portion which upon rotation causes axial displacement of the bearing surface in contact with the stud.

We claim: 
     
       1. A chain saw guide bar adapted for mounting to a chain saw having a chain saw housing including a projection positioned forward of a drive sprocket, said guide bar comprising: an elongated bar defining a bar length and having opposed side faces, a rear end, a forward end and peripheral guide edges for guiding a loop of saw chain from the rear end to and around the forward end and back to the rear end;   a mounting slot at the rear end of the bar adapted to receive the projection of the chain saw housing and to permit sliding movement of the bar relative to the projection and directed along the length of the bar toward and away from the drive sprocket; and   a configured cavity between the side faces and encompassing the mounting slot, said configured cavity including a formed portion, and a tensioning mechanism including a rotatable driver portion trapped between the side faces within the formed portion, said driver portion exposed in part through at least one of said side faces, and provided with a grip portion enabling an operator to manually rotate the driver portion, and a bearing portion of said tensioning mechanism projected into the mounting slot and including a bearing edge for engaging the projection, said bearing portion being advanced toward the projection by rotation of the driver portion for axial movement of the guide bar relative to the projection and thereby movement of the guide bar relative to the drive sprocket.   
     
     
       2. A chain saw guide bar as defined in claim 1 wherein the driver portion is a pinion having teeth and the bearing portion is a rack having teeth mated to the teeth of the pinion, said pinion rotatably driving the rack along the bar length and into engagement with the projection. 
     
     
       3. A chain saw guide bar as defined in claim 2 wherein the bearing edge of the rack is V or U configured to center the movement of the guide bar relative to the chain saw housing. 
     
     
       4. A chain saw guide bar as defined in claim 1 wherein the driver portion is a cam member having a center around which the cam member is rotated and the bearing portion is the periphery of the cam member which varies in distance from the center, said periphery in contact with the projection and extending the distance between the center and the projection as the cam member is rotated. 
     
     
       5. A chain saw guide bar as defined in claim 4 wherein the cam member is pivotal about an axis of rotation and the periphery increases in radial distance substantially through an entire rotation of the cam member. 
     
     
       6. A chain saw guide bar as defined in claim 1 wherein the driver portion is a cam member and the bearing portion is a slide member slidable along the mounting slot toward the projection, said cam engaging the slide member and upon rotation, camming the slide member against the projection. 
     
     
       7. A chain saw guide bar as defined in claim 6 wherein a hub portion projects from the cam member through the side face and defines an axis of rotation of the cam member. 
     
     
       8. A chain saw guide bar comprising: an elongated guide bar member defining opposed side faces and upper and lower edges having saw chain guide grooves, and rear and front ends, said rear end including a mounting slot extended axially along a length of the bar for mounting the bar to mounting studs on a chain saw housing;   a cavity provided in the guide bar member between the side faces, said cavity having a first portion extended axially along the length of the guide bar member and overlapping with and forward of the mounting slot, and a second portion configured to receive a pinion and an opening extending from the configured second portion to the exterior of the guide bar member at one of said side faces; and   a rack slidably positioned in the first portion of the cavity and a pinion rotatably positioned in the configured second portion of the cavity, said rack and said pinion provided with gear teeth in mating engagement whereby turning movement of the pinion produces sliding movement of the rack, and said pinion provided with a gripping feature accessible through the opening to enable turning of the pinion from the exterior of the guide bar member whereby, with the bar mounted on the chain saw housing, upon rearward sliding of the rack, a rearward end of the rack engages a bearing member provided on the chain saw housing to force forward sliding of the bar relative to the bearing member.   
     
     
       9. A chain saw guide bar as defined in claim 8 wherein the guide bar is mounted on the mounting studs of the chain saw housing, one of said studs providing the bearing member, said rack extended along the bar axis and the rear end of the rack being concave to induce centering of the rack and the guide bar relative to the studs for centering of the bar axis along a centering line defined by the studs. 
     
     
       10. A chain saw guide bar as defined in claim 8 wherein the pinion is loose fitting in the cavity and forced sliding of the rack against the bearing member creates binding of the pinion in the cavity and resistance to reverse turning of the pinion. 
     
     
       11. A chain saw guide bar as defined in claim 10 wherein the cavity is configured to provide a protruding edge for engagement by the gear teeth of the pinion. 
     
     
       12. A chain saw guide bar as defined in claim 8 wherein the gripping feature is a slot for receiving a blade of a tool which enables a user to turn the pinion. 
     
     
       13. A chain saw guide bar as defined in claim 8 wherein the bar consists of a center laminate and two side laminates, said first portion of the cavity provided in the center laminate and extended rearwardly at least the length of the mounting slot, the mounting slot provided in the guide bar having a width that is more narrow than the first portion of the cavity and the rack whereby the rack is retained within the first portion of the cavity as it is extended rearwardly along the mounting slot. 
     
     
       14. A chain saw guide bar as defined in claim 8 wherein upsets are provided in the travel path of the gear teeth of one of said pinion and said rack. 
     
     
       15. A chain saw guide bar as defined in claim 8 wherein a biasing member provided behind the pinion biases the pinion toward a forward position. 
     
     
       16. A chain saw guide bar as defined in claim 15 wherein a slot is provided in the guide bar rearward of the configured portion to form a depending finger that is resilient and provides said biasing member.